bromine prep reaction

[stratosphere]

I noticed in the inorganics chemical index there is no procedure for the prep of liquid bromine, so I thought I would contribute the method I have developed and “perfected” for possible inclusion in the index.

liquid bromine from KBr
Add 85ml 20% H202 (0.5mols h202) to 100ml of dH20.

To this add 60g KBr (0.5mols) and stir till dissolved.

(Will require a lot of stirring. Since KBr is hygroscopic you may need to oven dry it beforehand to ensure proper weight)

once the KBr is dissolved in the H20/H202 slowly add 80ml 12M (30%) HCl (1mol HCl).
At this point Br2 will form and the solution will turn reddish, some (mildly irritating) Br2 fumes will evolve so be cautious.

Other concentrations of H202 and HCl will work as long as the correct number of moles are used, although I suspect very dilute forms would give a poor yield.

At this point setup for distillation, I have attempted to extract the bromine from the water with DCM but this was not very effective.

Distill off the bromine by holding the temp of mixture at ~85C for about an hour until the red Br2 can no be seen condensing. The water will probably have a slightly yellow turbid appereance even after most of the bromine is removed. I recommend chilling the reciever in an ice bath while distilling to reduce fuming.

To dry the condensed bromine pour it in a small graduated cylinder. Use a pipette to add about 1 ml of conc. H2S04, mix gently with pipette tip. When H2S04/H20 de-emulsify and float to top use pipette to remove them.

Yield: 10ml Br2 = 31g Br2 = 0.4mols Br
Percentage Yield = 80% relative to Bromine

[Rhodium]

I would strongly suggest to chill the recieving flask in an ice-bath while distilling.

Also, as you acidify with HCl rather than H2SO4, what prevents the formation of BrCl - thermodynamics?

[stratosphere]

actually i did chill the reciever while distilling, will edit accordinly.

the yield was 80% so maybe some of the missing portion was BrCl which boils at 5C.

ive tried h2SO4 but noticed it was catalyzing the decompostion of h202. whether this was due to impurities in it (it was tech grade), or is intrinsic i don't know.

so i guess it would be neccasary to hold the Br2 at a little over 5C to allow the boil off of BrCl, or to use H2S04 and deal with whatever decomp it causes.

[Nicodem]

No BrCl can be formed if you use at least a slight excess of the KBr over the H2O2 as BrCl reacts with Br^-. If the oxidant is in exces you get the bromic acids (HBrO, HBrO3) and loose on the yield. Instead of H2O2 you can also use NaOCl, KMnO4, MnO4 or many other oxidants. Check also the first preparation in

Post 472828

(Nicodem: "2,5-Dimethoxybromobenzene Chloromethylation", Novel Discourse) for using the in situ preparation of bromine from KBr in a two phase system. It is more economic for KBr and very handy for the bromination of activated aromatics. But off course it is useless for the bromination of acid soluble compounds like phenylethylamines.

[stratosphere]

isn't that backwards?

meaning a excess of Br- would favor Br2 over BrCl.

if there is alot of Br-'s running around then BrCl would favor reacting with them to form Br2, if there was not enoughBr-'s  then the BrCl would have nothing to react with and would be more likely to just distill off.

[Antibody2]

Ab2 usually makes his Br2 the opposite way, 1st reacting KBr or NaBr with H2SO4 to form HBr, then add the H2O2 to the HBr to evolve the Br2. The H2O2 addition is exothermic so the addition rate needs to be monitored or the condenser can't keep up, external heat is only required at the very end.

also runs a hose out the window off a vacuum adapter on the reciever to vent any Br2 fumes

[lugh]

Here's the article from Thorpe's on bromine, which may bee useful  

[Nicodem]

Stratosphere, I apologize if my post was not written clear enough for you but please read it carefully and tell me where it is written backwards.
Anyway, when you did your inorganic chemistry research did you perhaps come across any really easy preparation of BrCl from KBr? BrCl would be a really useful brominating reagent as it is more electrophilic/reactive than Br₂. BrCl decomposes to HBrO and Cl^- in water but maybe the equilibrium can be shifted back to BrCl in conc. hydrochloric acid while the BrCl being extracted with DCM?

[Vitus_Verdegast]

when you did your inorganic chemistry research did you perhaps come across any really easy preparation of BrCl from KBr?

Bubble chlorine through a saturated solution of sodium (or potassium) bromide. The bromide ions will be oxidised into bromine, some of which will further react with the chlorine to produce bromine monochloride.

Bromine monochloride boils at 5°C, and so if the sodium bromide solution is kept at about 10°C (in order to get the product into gas phase, whilst minimising evaporation of the bromine), the outgoing gas should consist of the product mixed with excess chlorine. This can then be seperated out by cooling the gas.

http://www.sciencemadness.org/talk/viewthread.php?tid=1091

[sYnThOmAtIc]

VITUS--- So this means that the ultrasimple method I was looking into for making Br2 by bubbling Cl2 into bromine solution is not a good idea as it makes BrCl?? Is there any way to eliminate this? As I was reading that the industrial process most commonly employed was using Cl gas?? I jsut liked it casue it sounded so simple bubble then distill. Rather than touchy oxidations and such.

[hydroxyindolent]

Has anyone tried simply gently refluxing an appropriate molar solution of H2SO4, alkali bromide, Mn02 or KMn04, then distilling Br2 into a flask with CaCl2, then distilling again into an iced flask to afford dry liquid bromine?

(Adapted from an antiquated text on element isolation...)

[stratosphere]

Nicodem>>

what you wrote suggested to me that you were implying an excess of Br- would favor the formation of BrCl, when in fact the opposite is true. meaning an excess of Br- to Cl2 (i.e. more then 2mols of Br- for every mol of Cl2) would be favorable to bromine production.

also when rechacking my lab notes agianst my write up i noticed a mistake. the amount of H202 and HCl should be halved. that is the correct amounts are 60g KBr, 40ml 20%H202, 40ml 12M HCl.

[stratosphere]

Hydroxyindolent>>

adding alkali bromide to concentrated H2S04 gives a messy stinky mix of HBr Br2 S02 and H20.

[Antibody2]

if you are going to make HBr by adding H2SO4 to NaBr or KBr you need some water, or the evolved HBr will be a gas not the constant boiling 48% HBr.

and if Br2 is evolved in that reaction it means it wasn't cooled properly or the addition was too fast.

[Vitus_Verdegast]

making Br2 by bubbling Cl into bromine solution is not a good idea as it makes BrCl2??

What do you mean by bromine solution? Bromine water?
Or do you mean a solution of alkali metal bromides?
(please, try to spell correctly   )

Bubbling Cl₂ into a solution of Br^- (or into bromine water) will give BrCl, yes, as the formed bromine will react with chlorine. Read up on interhalogen compounds in an inorganic chemistry textbook.

Also, BrCl will form a solid hydrate BrCl.4H₂O when chlorine is passed into bromine covered with water.

Why not just simply distill off bromine from a mixture of a bromide, acid and oxidizing agent as described in this thread and elsewhere?

[sYnThOmAtIc]

I meant a saturated NaBr or KBr in water. Then bubbling chlorine gas in to liberate the bromine from the alkali then distilling off the released Br2. I read on the internet in a bref industrial process that chlorine liberates free bromine from all sources. And that the common industrial method was to pass Cl2 gas up a column with  falling KBr and that the bromine was removed using ether. Just seemed easier and quicker than a multistep reaction that seems touchy.

Because, I don't have access to concentrated H2O2! Only oxone and maybe permanganate if i find it at the hardware store and I haven't seen any mention to their use. I know oxone liberates some Br2 from an alkali bromide but unsure of side reactions or products or else the package wouldn't say bromine activator.. Just don't know how much to use how to add and such. Don't even know if it is strong enough to do the job completely.

Generating chlorine from HCL and bleach and bubbling it through a saturated water/NaBr seemed simple and more OTC. Than 20-50% H202, manganese dioxide, etc, I may have access to permanganate from the hardware store but haven't confirmed it. Only oxone for sure and 3% H2O2. Looking to get elemental Br2 as product.

[hydroxyindolent]

Indeed, however if you note my post carefully, the presence of the MnO2 or KMn04 oxidizes the HBr to Br2, which then distills over.

[sYnThOmAtIc]

Yes man I'm very well aware THAT. Like I said I don't have access to those!! DID you not MY post carefully?

I have read a many different methods of producing this substance. But like I SAID, I don't have access to any stong oxidisers other than oxone... My post was about OXONE/Cl2.

I definately can't get manganese dioxide and not sure about permanganate like I said earlier, newbee. Your post was noting new. Heatng an alkali bromide with mno2 was the first method on the long list of mehtods I have sitting here, which I specifically mentioned in the last paragraph! Though, not much use to me is it? If it were of interest or possibility I would not have posted about alternatives!!!!

Yeah I guess you didn't see that long sentence at the end there... In ther before you posted..

Damn, I thought I was bad about that kinna shit.

[sYnThOmAtIc]

Bromine
Bromine, Br, is a red volatile liquid at room temperature, having a red brown vapour and a member of Group VIIb (i.e. the Halogen Group of elements) of the periodic table.
Atomic Number : 35
Atomic Mass : 79.909
Melting Point : -7 degC
Boiling Point : 58 degC
Density : 3.1
It forms compounds in which its oxidation states is 1, 3, 5, or 7.
The liquid is corrosive and harmful to human tissue and bromine vapour irritates the eyes and throat.
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Discovery
Bromine was discovered by A J Balardin 1826AD, by the action of Chlorine on the residues (i.e. Bromide salts) after the crystallisation of the salt from the salt-marshes of Montpellier.


      NaBr    +    Cl2    ==>    NaCl    +   Br2   

Balard also demonstrated that the liquid was an element and he suggested the name Bromine (Greek, stench) for the liquid.


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Occurrence
Because of its reactivity, Bromine does not exist in the free elemental state in nature, but small quantities are combined in many silver ores.
Compounds of Bromine also occurs in marine animals and plants.
Bromide salts are found in seawater and in the salts deposits in Strassfurt.

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Extraction
Bromine occurs primarily as bromide salts (e.g. Sodium Bromide, NaBr) in sea-water. On passing a stream of chlorine gas through a solution containing Bromide Ions, Br(-), free elemental bromine is released.


   2 Br(-)   +   Cl2   ==>   Br2   +   2 Cl(-)



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Preparation
Bromine can be prepared in the laboratory by heating Potassium Bromide, KBr, with dilute Sulphuric Acid, H2SO4, and Manganese Dioxide, MnO2.


           2 KBr   +   MnO2   +   3 H2SO4   ==>   Br2   +   2 KHSO4   +   MnSO4   +2 H2O



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Manufacture
Bromine is manufactured industrially by allowing a solution of Potassium Bromide to flow down a tower, against a stream of Chlorine gas rising up through the tower.


        2 KBr   +    Cl2    ==>    Br2   +    2 KCl   



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Properties
Bromine is a volatile dense mobile reddish-brown liquid, which readily gives a brown toxic vapour with a disagreeable irritating odour.
Bromineresembles Chlorine in many of its properties, but it is less reactive.
A solution of Bromine in water is called Bromine Water, which is used as a test reagent in organic chemistry to identify unsaturated compounds.
Bromine combines directly with most elements although heat or a catalyst is often necessary to start some reactions.


                   H2   +   Br2   ==>   2 HBr   

      2 Na   +   Br2   ==>    2 NaBr   


Bromine reacts with water to form a mixture of Hydrobromic Acid, HBr, and Hypobromous Acid, HBrO.


      Br2   +   H2O   ==>   HBr   +   HBrO   


Bromine liberates Oxygen when the resulting solution is heated or exposed to strong sunlight.


      2 HBrO   ==>   2HBr   +   O2   


Bromine reacts with alkalis in a similar way to Chlorine. Bromine also displaces free elemental Iodine from solution of Iodide Salts, I(-).

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Reactions

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Uses
Bromine is used in a vide range of industries :
in the manufacture of 1,2-DibromoEthane, CH2BrCH2Br, which is used as a petrol additive to prevent lead being deposited in the cylinders (i.e. from the anti-knock agent, Tetra-Ethyl Lead, Pb(C2H5)4),
in the manufacture of compounds used in photography (e.g. Silver Bromide, AgBr, which is the light sensitive material in film),
in the manufacture of dyestuffs and drugs,
in the analytical laboratory in testing for unsaturation in organic compounds, where bromine adds across the multiple bonds of unsaturated compounds,
as a disinfectant, adsorbed in sticks of a diatomic brick,
in making dyes, and
in gold extraction

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Detection and Analysis
Bromine is detected by the brown colour of its vapour, and by its action on Iodide salts, (e.g. Sodium Iodide, NaI), which are oxidises to free elemental Iodine.


      2 NaI    +    Br2    ==>   2 NaBr    +     I2   

The Iodine liberated in this reaction turns starch indicator solution to a blue colour.

[ADDkid]